Magnetic core composition and method of producing the same



Patented Oct. 28, 1953 MAGNETIC CORE COMPOSITION AND METHOD OF PRODUCING THE SAME Godshalk Berge, Chicago, Ill., assignor to Aladdin Industries, Incorporated, Chicago, 111., a. corporation of Illinois No Drawing.

Application January 3, 1949,

Serial No. 69,044

Claims. 1

This invention relates to magnetic cores for use in inductance tuning coils and transformers or other elements in electrical circuits and particularly for use in high frequency circuits in the television or FM range of about 76.5 to 108 me, an in excess of 200 me.

It is an object of this invention to produce a magnetic core having good operating characteristics at the frequencies of operation.

More specifically, it is an object of this invention to produce and provide a method for producing a magnetic core for tuning an inductance coil over a satisfactory tuning range in the region of 100 and 200 me. and above, while obtaining a Q of at least 80 which remains substantially constant over the entire useable range, and negligible thermal drift, measured in percent per degree centigrade, while operating over the range for which it is intended.

Another object is to produce a magnetic core having desirable operating characteristics and to provide a method for expediently and economically producing the same from commercially available raw materials combined in a novel manner to provide a molecular arrangement that imparts the desired characteristics.

A further object is to provide a new compound for the manufacture of magnetic cores which includes the combination of certain new complex compounds with various additives that beneficially alter the characteristics of the core to meet predetermined specifications.

Many tests have shown that the Q of mag-'- netic cores heretofore produced and which are satisfactory at certain frequencies is materially lowered beyond useable values at higher frequencies. that magnetic cores having satisfactory operating characteristics at broadcast frequency are wholly unsuitable at higher frequencies, such as the FM or the television range. The same considerations apply to magnetic cores designed to have satisfactory characteristics at television or FM frequency ranges but which were found to be unsatisfactory at frequencies of 200 me. or more.

For example, a magnetic core formulated of cobalt oxide, nickel oxide, iron oxide, zinc oxide, vanadium oxide, and magnesium zirconate, mixed in proportion to produce a stable composition, has a Q of 90 at frequencies of 108 to 76.5 me. when the first two metal oxides are separately reacted with the necessary molecular equivalents of iron oxide to form substantially stable salts. When measured at 200 me. however, the Q value dropped to between and 40, depending on the proportion of materials in the final product.

In most cases, the drop in Q is so great The importance of higher frequencies in communication is continuously mounting, and it is desirable to have magnetic cores which have good operating characteristics at ultra-high frequencies of 200 me. or more. It is most desirable to be able to fabricate a magnetic core which is satisfactory for use through a wide range of frequency, including 76.5 to 108 mc., to 213 mc., over 213 mc., and even at lower radio frequency ranges, such as the broadcast range. Formulation of a magnetic core having these characteristics is an important object of this invention. a

To accomplish these results, I provide as an essential ingredient for the core composition a material which might be termed a substantially neutral complex compound by the reaction of either the full complement of cobalt oxide or nickel oxide, or both, with sufficient iron oxide to give a reaction corresponding to the following:

0020: F620: F6204 or F8204 or 2 FezOH-O NiO N10 3. NiO

NizOa 203 N10 F9204 0! FGOI'I'O NiO The metal oxides may be designated as being present in amounts corresponding to the equal molecular equivalents, but, for all practical purposes, variations of 10 percent from theory are permissible. It will be understood that the reaction of cobalt oxide and nickel oxide together with iron oxide will not result in the complete conversion to the complex indicated in Equation 2, but some of the complexes in Equations 1 and 3 will be formed in minor amounts.

To carry out the formation of the complex, the metal oxides in finely divided form are intimately mixed together and subjected to firing at 2,000 to 2,500 F. for one to five hours, depending on the temperature used. The reaction product is a hard friable mass which can be finely divided to form a raw material for magnetic core formation, the reaction product having exceptionally good magnetic properties.

Although magnetic cores might be formed of the reaction product of cobalt oxide with iron oxide in amounts to produce the complex compound or by the reaction of nickel oxide with iron oxide in the desired amounts, cobalt and nickel oxides are not considered to be full equivalents because the characteristics of each in high frequency circuits are in variance in the range of 100' to 200 mc. A complex compound formed of the two in various proportions gives improved results and a compound formed of the two in substantially equal proportions gives very excellent results through the entire range.

For example, the complex indicated by Equation 3, when compounded into a core, has a range between 108 to 88.5 mc. and a Q of 18, while the corresponding complex produced by the reaction of Equation 1 gives a range of 108 to 104 me. with a Q of 171. Since the Q value of the cobalt complex is in excess of that normally required, the range can be expanded at higher frequencies until the corresponding drop in Q is at a limiting value. Thus, with this composition, a magnetic core having acceptable properties may be produced for use in frequency ranges over 200 mc., and probably over 500 me.

Compounding for magnetic core formation may be carried out by admixing the finely divided reaction products with a small amount of binder and molding the mixture under relatively high pressure to core shape. As the binder, use may be made of the organic resinous materials, such as the phenol-aldehyde resins, urea-aldehyde resins, vinyl polymers and copolymers, polystyrenes, polyacrylates, elastomers, and the like. These materials are generally heat sensitive but serve to impart cohesive strength to the molded product until well beyond their thermal decomposition temperature of about 400 to 500 F. When organo silicons or silicates are used as the adhesive component, it is conceivable that some cohesion may remain after heat treatment. In any event, binder content in amounts ranging from about 2 to percent may be used depending on the type of binder and the characteristics of the core materials, but ordinarily 2 to 3 percent is sufiicient.

The molded composition is heat treated by subjecting the mass to a temperature in the range of 1,800 to 2,350 F. for one-half to two hours, depending on the amount of material being handled. During heat treatment, one or more of the constituent materials may function as an agent to bond the particles to mold form. Inequalities in density and permeability following molding are compensated during heat treatment by resulting shrinkage ultimately to produce a product having the very desirable property of equal permeability throughout. Best results are secured when the rate of cooling from heat treating temperature is controlled to secure an annealing effect, such as by the reduction of temperature in 100 F. per hour decrements.

Zinc oxide may be used with these complex compounds to extend the range without causing excessive harm to the Q values. To prevent harmful alteration of the complex compound by the zinc oxide, as by atomic displacement, it is expedient first to neutralize the zinc oxide by thermal reaction with iron oxide in substantially equal molecular amounts to convert the greater portion of the zinc oxide to a stable salt, such as zinc ferrite. In the event that the addition of 'zinc oxide is made directly to the finely divided complex compound in the mixing step prior to molding, further iron oxide should be added in an amount sufficient to neutralize the base and to minimize the disturbing effect it might other- Wise have on the complex compound. The addition of zinc oxide to a nickel-cobalt-iron complex may be illustrated by the following examples:

ExampleI Material Percentage Nickel oxide 18.6 Cobalt oxide 18.6

Zinc oxide 9.1 Iron oxide 53.7

The nickel oxide and cobalt oxide are fired at 2200 F. for three hours with the necessary equimolecular equivalents of iron oxide. The reaction product is cooled at room temperature and reduced to finely divided form. The reaction product is intimately mixed with the zinc oxide and the remaining iron oxide and compounded with about 2 percent phenolformaldehyde A- stage resin. The mixture is molded to core formation at about 2,000 pounds per square inch pressure and then subjected to a heat treatment for one hour at 2200 F. The heat treated product is cooled to room temperature in increments of F. per hour and then ground down to a finished product. The characteristics of the core produced by the above are as follows:

Range 108 to 98.8 mc., Q 142 Range 200 to 181 mc., Q

Example II To 60 parts of a complex compound manufactured of nickel oxide with iron oxide in equimolecular proportions under the conditions set forth in Example 1, 40 parts of the thermal reactions products of zinc oxide with iron oxide in equal molecular portions are added. The materials are mixed with about 2 percent organic binder and molded to core formation, and annealing of a desirable character is secured by subjecting the molded product to 2,100 F. for one hour and then cooling to room temperature in 100 F. per hour increments. The product of this reaction has:

Range 108 to 81 mc., Q '72 This is to be compared with the range of 108 to 104 me. and Q of 171 secured by the complex compound along without the zinc ferrite addition. Thus, there is illustrated the efiect of zinc oxide to extend the range but with a permissible lowering of the Q value.

Other improved characteristics are secured by the addition of vanadium oxide with or without the addition of zinc oxide or its iron salts. Vanadium oxide carries the range still further when used in amounts up to 5 percent. Although increased amounts may be used, the extension of range does not warrant the increased cost and, therefore, I prefer to use less than 5 percent, although as much as 10 percent by weight has been successfully employed. To minimize the effect of vanadium oxide on the complex compound, additional iron oxides are added in sufficient amount for neutralization purposes. It is believed that the possible reaction product in this instance may be ferro-vanadanite.

An important feature of this invention resides in the use of magnesium zirconate to lower the thermal drift of the core, particularly when made of the compositions described. Magnesium zirconate is unlike other elements or compounds heretofore used for reducing thermal drift in corresponding systems because it apparently is able at the same time to support the Q values at their desirable level. The desired effect is secured when at least 4 percent of magnesium ,zirconaute is employed, but best results are se cured when the magnesium zirconate is present in amounts ranging from 6 to 12 percent by weight. To a, limited extent, magnesium zirconate may be substituted by lead titanite. Substitution, however, seldom exceeds 25 percent.

When measured by their oxides, the amount of materials that may be used to formulate a magnetic core embodying all of the elements described are as follows:

5 to 20 parts cobalt oxide 10 to 25 parts nickel oxide Less than parts zinc oxide 40 to 65 parts iron oxide Less than 10 parts vanadium oxide Less than 12 parts magnesium zirconate The following examples are given by way of illustration but not by way of limitation to illustrate the features of this invention:

Example III The cobalt oxide, nickel oxide, and equi-molecular equivalents of iron oxide are fired at 2,400 F. for one hour to form the complex compound. Upon cooling to room temperature, the thermal reaction products are ground to powdery form. Admixture is made with the zinc oxide, vanadium oxide, magnesium zirconate, the remaining iron oxide, and 4 percent phenolformaldehyde binder. Molding to core formation is effected by a suitable press operating under about 2,000 pounds per square inch pressure. The molded product is heat'treated at a temperature in the range of 2100 to 2350 F. for one and one-half hours, and then it is cooled down slowly under room conditions. The characteristics of the resulting core areas follows:

Range 108to81 mc., Q 100 Negligible thermal drift s: a a V 1 Range 200 to 147 mc., Q 85 Negligible thermal drift Example IV Material Percentage Iron oxide 58.3 Cobalt oxide 9.2 Nickel oxide 13.0 Zinc oxide 12.0 Vanadium oxide 1.5 Magnesium zirconate 6.0

The materials are combined in the manner described in Example III and the product secured therefrom has the following properties:

Range 108 to 79 mc., Q 98 Negligible thermal drift Range 200 to 144 mc., Q 80 Negligible thermal drift ExampleV' Material: 7 Percentage Iron oxide 56.6 Cobalt oxide 8.7 Nickel oxide 13.6 Zinc oxide 12.0 Vanadium oxide L 1.1 Magnesium zirconate 6.0 Lead titanite 2.0

The materials are treated and combined inthe manner described in Example III. The resulting product has the following characteristics:

Range 100 to 81 1110., Q 100 Negligible thermal drift 1: =1

Range 200 to 150 mc., Q Negligible thermal drift Example VI Material: Percentage Iron oxide 57.3 Cobalt oxide 8.7 Nickel oxide 13.6' Zinc oxide 12.0 Vanadium oxide" .4 Magnesium zirconate 6.0 Lead titanite 2.0

The materials are combined in the manner described in Example III and the product secured therefrom has the following properties:

Range 108 to '79 mc., Q Negligible thermal drift a s a Range 200 to mc., Q 84 Negligible thermal drift It will be manifest that I have discovereda new complex compound for the manufacture of magnetic cores which may be used at various frequencies ranging from low to extremely high frequencies with excellent characteristics with respect to the extent of the'range, the Q value, and thermal drift. Importance is also attached to the use of magnesium zirconate in core composition materials to reduce the thermal drift while still being able to support the Q values of the core elements. I

It will be understoodthat the features of my invention may be embodied in the production of cores for radio frequency cycles for frequencies in the television and FM-range and for ultimately high frequencies in excess of 200 mc. It will be further understood that numerous changes may be made in the amounts, the order of addi tion, and the manner of treatment of the materials within reasonable limits without departing from the spirit of the invention, especially as defined in the following claims.

I claim as my invention:

1. A magnetic core containing a complex compound comprising the product of the reaction of a metal oxide selected from the group consisting of Ni203, C0203 and mixtures'thereof with FezOa in substantially equal molecular proportions at 7 about 2000-2500 F. for 1-4 hours, zinc ferrite, vanadium ferrite and magnesium zirconate in which the materials when calculated on the basis of their oxides are present in amounts ranging from 5-20 parts by weight cobalt oxide, 10-25 parts by weight nickel oxide, 40-60 parts by weight iron oxide, a small amount up to about 15 parts by weight zinc oxide, a small amount up of the magnesium zirconate.

' A agnetic core as claimed in claim 1 in which the magnesium zirconate may be substituted by a small amount up to about 25 percent of its weight with lead titanite.

3. The method of manufacturing magnetic cores comprising reacting NizOs and C0203 in about equal proportions with about a molecular equivalent of F6203 at 2000-2500 F. for 1-4 hours to form a complex having magnetic properties, mixing the complex with a small amount up to about 15 percentzinc oxide, a small amount up to about 10 percent vanadium oxide, a small amount up to about 12 percent magnesium zirconate and suiiicient additional iron oxide to react with the zinc and vanadium oxides to form the corresponding ferrites, mixing a binder with the material in amounts ranging up to 10 percent by weight, molding the compound to core shape, and heating the treated molded product at a temperature between 2100-2350 F; for at least one hour and then slowly cooling the heated product to room conditions.

4. The method as claimed in claim 3 in which the zinc oxide is first thermally reacted with suilicient of the additional iron oxide at 2000- 2500 F. to form the corresponding zinc ferrite.

5. The method as claimed in claim 3 in which the materials when calculated as their original oxides are present in amounts ranging from 5-20 parts by weight C0203, 10-25 parts by weight NizOa, 40-60 parts by weight F8203, a small amount up to about 10 parts by weight vanadium oxide, a small amount up to about 15 parts by weight zinc oxide and a small amount up to about 12 parts by weight magnesium zirconate.

6. A magnetic core containing the complex thermal reaction, product of a metal oxide selected from the group consisting of C0203, Nozos and mixtures thereof with F8203 in substantially equal molecular proportions at a temperature of 2000- 2500 F. for about 1-4 hours, combined with the product of the reaction under similar conditions has subsequently been heated to a temperature within the range of 21002350 F. for at least one hour.

'7. In the method of manufacturing magnetic cores, the steps of reacting an oxide selected from the group consisting of NizOa, C0203 and mixtures thereof with substantially equal molecular equivalents :10 percent of F6203 at a temperature within the range of 20002500 F. for about l-4 hours to form a stable reaction product having magnetic properties, compounding the reaction product in finely divided form with a small amount up to about 15 percent by weight zinc oxide and a small amount up to about 10 percent by weight vanadium oxide and suflicient iron oxide to react with the zinc oxide and form the corresponding zinc ferrite, molding the materials to core shape and then heating the molded mass at a temperature within the rang of 2150-2350 F. for at least one hour.

8. In the method of manufacturing magnetic cores the steps of reacting an oxide selected from the group consisting of NizOs and C0203 and mixtures thereof with substantially equal molecular proportions :10 percent of F6203 at a temperature within the range of 2000-2500 F. for 1-4 hours, compounding the reaction product in finely divided form with a small amount up to about 12 percent by weight magnesium zirconate, a small amount up to about 15 percent by weight zinc oxide and a small amount up to about 10 percent by weight vanadium oxide and iron oxide in an amount sufficient to react with the zinc oxide and vanadium oxide to form the corresponding zinc and vanadium ferrites, molding the composition to core shape and heating the molded mass at a temperature within the range of 2100-2350 F. for at least one hour.

9. A magnetic core formed by the method of claim 3.

10. A magnetic core formed by the method of claim 7.

GODSHALK BERGE.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Kato et al Apr. 9, 1935 Snoek Oct. 26, 1948 OTHER REFERENCES Number 

1. A MAGNETIC CORE CONTAINING A COMPLEX COMPOUND COMPRISING THE PRODUCT OF THE REACTION OF A METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF NI2O3, CO2O3 AND MIXTURES THEREOF WITH FE2O3 IN SUBSTANTIALLY EQUAL MOLECULAR PROPORTIONS AT ABOUT 2000-2500* F. FOR 1-4 HOURS, ZINC FERRITE, VANADIUM FERRITE AND MAGNESIUM ZIRCONATE IN WHICH THE MATERIALS WHEN CALCULATED ON THE BASIS OF THEIR OXIDES ARE PRESENT IN AMOUNTS RANGING FROM 5-20 PARTS BY WEIGHT COBALT OXIDE, 10-25 PARTS BY WEIGHT NICKEL OXIDE, 40-60 PARTS BY WEIGHT IRON OXIDE, A SMALL AMOUNT UP TO ABOUT 15 PARTS BY WEIGHT ZINC OXIDE, A SMALL AMOUNT UP TO ABOUT 10 PARTS BY WEIGHT VANADIUM OXIDE, AND A SMALL AMOUNT UP TO ABOUT 12 PARTS BY WEIGHT OF THE MAGNESIUM ZIRCONATE. 